Synergistic herbicidal composition comprising vinegar and lemon juice

ABSTRACT

A herbicidal composition, which can be formulated for selective or total kill of vegetation of as a growth regulator, comprises a synergistic combination of acetic acid and citric acid.

REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent application Ser. No. 08/190,201 filed Aug. 6, 1992 now U.S. Pat. No. 5,573,997.

FIELD OF INVENTION

The present invention relates to herbicidal compositions comprising synergistic mixtures of acetic acid and citric acid.

BACKGROUND TO THE INVENTION

Many herbicidal compositions exist which are effective in killing all vegetation or selective vegetation. Many are based on sophisticated chemicals, some of which are toxic to other life forms.

Acetic acid exhibits some effect as a herbicide while citric acid at high concentrations exhibits some effect as a herbicide. There has been suggestions to use acetic acid as a herbicide, e.g. DE 4 030 687 (Kast), which describes such use alone or in combination with tensides.

SUMMARY OF INVENTION

The applicants have now found that synergistic compositions of acetic acid and citric acid may be employed as a contact herbicidal composition. The essential components of the herbicidal compositions are edible materials and, hence, can be safely applied to vegetation without risk of harm to animals, including humans.

Accordingly, in one aspect, the present invention provides a novel herbicide composition which comprises an aqueous solution of a synergistic mixture of acetic acid and citric acid. In an additional aspect of the present invention, there is provided a method of controlling post-emergent vegetative growth, which comprises applying to the vegetative growth an aqueous herbicidal composition comprising acetic acid and citric acid. The citric acid is present in the composition in a herbicidal activity enhancing amount and the acetic acid and citric acid are present in the composition in proportions to achieve a desired degree of kill to the vegetative growth.

By itself, acetic acid does not exhibit broadleaf weeds and grasses selectivity. However, in combination with citric acid, as provided herein, it is possible to selectively control a number of annual and perennial weeds, including broadleaf weeds in established lawns and pastures.

The herbicidal composition provided herein is a contact herbicide, which may be applied by spraying above-ground portions of the weeds that it is desired to kill, providing a simple mode of administration.

The compositions of the present invention rapidly and consistently kill above-ground parts of weeds. Plant injury is observed within a few hours of application of the compositions of the invention and plant death within a few days.

The compositions of the invention may be employed to kill and control a wide variety of annual and perennial broadleaf weeds and grasses. Representative vegetative growth includes:

    ______________________________________                                         Annual Broadleaf Weeds                                                                              Annual Grasses                                            ______________________________________                                         Black medic          Crab qrass                                                Chickweed            Foxtail spp.                                              Cinquefoil (rough)                                                             Lamb's-quarters                                                                Oxalis spp.                                                                    Ragweed spp.                                                                   ______________________________________                                         Perennial Broadleaf Weeds                                                                           Perennial Grasses                                         ______________________________________                                         Cinquefoil (Silvery) Quackgrass                                                Dandelion            Bluegrass                                                 Plantain spp.                                                                  Toadflax                                                                       Tufted vetch                                                                   Wild carrot                                                                    ______________________________________                                    

The compositions of the present invention further are effective as growth regulators for a variety of plants, inhibiting or stimulating growth of the plants according to the ratios of acetic acid and citric acid used.

GENERAL DESCRIPTION OF INVENTION

The compositions of the invention can be formulated to effectively kill all vegetative growth, including normally hard-to-kill weeds as well as grasses, in a rapid period of time. Alternatively, the composition may be formulated as a selective herbicide, for example, to kill common lawn weeds, while leaving the grass unaffected. The composition of the invention also is useful as a defoliant.

The composition of the invention comprises a synergistic combination of acetic acid and citric acid. The acetic acid component conveniently is provided by domestic white vinegar while the citric acid is conveniently provided by lemon juice or the juice of another citrus fruit. Industrial sources of these components also may be used in formulating the composition of the invention.

The compositions of the invention may be formulated as concentrates comprising glacial acetic acid and citric acid in the desired ratio dissolved in water, which then may be diluted to the desired strength for use. For example, a concentrate may be prepared by combining 250 g of glacial acetic acid, 125 g of citric acid (i.e. a weight ratio of acetic acid to citric acid of 2:1) with 625 g of water, to provide a concentrate containing 25 wt % acetic acid and 12.5 wt % citric acid. The composition may contain 620 g of water and 5 g (0.5 wt %) of a wetting agent. Another useful formulation of concentrate provided herein comprises:

160 g acetic acid

40 g citric acid

800 ml water

These concentrates then may be diluted by adding water to provide an aqueous herbicidal composition having the desired concentrations of acetic acid and citric acid for application to the vegetative growth to be killed.

By experimentation, it is possible to determine the degree of dilution required for specific properties of the composition for varying proportions of acetic acid and citric acid.

Although acetic acid alone exhibits some effect as a herbicide as mentioned above, the presence of small quantities of citric acid according to the present invention considerably enhances the effect. Citric acid at high concentrations exhibits some effect as a herbicide, but at the low concentrations provided herein considerably enhances the herbicidal properties of the acetic acid, thereby providing a synergistic herbicidal effect.

The weight ratio of acetic acid to citric acid in the composition of the invention may vary from about 10:1 to about 1:0.5, preferably about 4:1 to about 1:1. In general, with the presence of an increasing quantity of citric acid for the same quantity of acetic acid, there is an increasing herbicidal activity to a maximum level of such activity, at which addition of further quantities of citric acid produces no further herbicidal effect. The composition in use may contain up to about 10 wt % of acetic acid, preferably about 1 to about 5 wt.%. The composition in use may contain about 0.25 to about 5 wt % citric acid.

The herbicidal activity of the combination of acetic acid and citric acid may be enhanced further by the presence of small quantities of wetting agents to enhance the wetting ability of the compositions of the invention on the vegetative growth to which the aqueous herbicidal composition is applied. Such wetting agents preferably are edible emulsifiers.

A particularly-useful composition according to the invention comprises about 2 parts by weight of vinegar (acetic acid) and about 1 part by weight of lemon juice or other citrus fruit juice (citric acid). This composition is diluted with water to provide the composition ready for use. The degree of dilution of the composition determines whether the herbicidal composition will kill all vegetation to which it is applied and whether it is selective.

One composition which has been found useful as a total vegetation kill composition comprises:

500 mls of vinegar (acetic acid)

250 mls of lemon juice (citric acid)

750 to 1250 mls of water

If the dilution is increased to about 2300 mls of water, the composition becomes a selective herbicide. Too much dilution, however, results in a composition having no herbicidal properties. For example, dilution by 5000 mls of water produces a composition which has no herbicidal response.

Another useful composition according to the invention comprises:

10 wt. % glacial acetic acid

5 wt. % citric acid

85 wt. % water.

In one preferred aspect of the present invention, there is provided an aqueous herbicidal composition for contact kill of vegetative growth, consisting essentially of:

acetic acid in an amount of from about 2 to about 10 wt % and

citric acid in an amount of from about 1 to about 6 wt %,

said acetic acid and citric acid being present in a synergistic weight ratio of about 1:0.1 to about 1:0.8,

said composition being in fully diluted form ready to apply to post-emergent vegetative growth by spraying onto the vegetative growth. Such composition may be prepared by dilution with water from concentrate. A small amount of a wetting agent, up to about 0.5 wt %, may be present.

The composition of the invention is composed of natural and edible components, namely acetic acid and citric acid and hence, not only is efficacious as a herbicide, either for total or selective kill of vegetation, but is safe to use. In contrast, most herbicides require chemical synthesis and exhibit toxic side effects on animals.

The present invention is illustrated further by the following Example:

EXAMPLE

This Example illustrates the synergistic effect of acetic acid and citric acid in herbicidal compositions.

Field corn, Vat. Trucker's Favourite, was used as a representative test species, since the combination of acetic acid and citric acid is a non-selective herbicide and field corn is a fast growing plant, easily grown under greenhouse conditions and is representative of grass or weeds.

Field corn was direct seeded into four inch paper pots containing HYPONEX®, a soil based growing medium. One seed was planted per pot. The pots were then incubated in a greenhouse. Plants were watered at least once daily on an as-needed basis. Greenhouse temperatures ranged from 62° to 89° F. throughout the growth and test period. Seed germination occurred within 4 days of planting. Field corn was at the two leaf stage (14 days after planting) at the time of treatment.

The experiments consisted of the following compositions:

(1) Product A (acetic acid) at 10, 8.0, 6.0, 4.0 and 2.0 wt %

(2) Product B (citric acid) at 6.0, 4.8, 3.6, 2.4 and 1.2 wt %.

(3) Mixtures of Product A+Product B at five levels, at a weight ratio of acetic acid to citric acid of 1:0.6:

    ______________________________________                                         A  B                                                                           ______________________________________                                          10.0 + 6.0%                                                                   8.0 + 4.8                                                                      6.0 + 3.6                                                                      4.0 + 2.4                                                                      2.0 + 1.2                                                                      ______________________________________                                    

(4) Mixtures of Product A+Product B at five levels, at various ratios of acetic acid to citric acid:

    ______________________________________                                                A  B     Ratio                                                          ______________________________________                                                 4.0 + 3.2%                                                                             1:0.8                                                                 4.0 + 1.2                                                                               1:0.3                                                                 4.0 + 0.8                                                                               1:0.2                                                                 4.0 + 0.4                                                                               1:0.1                                                          ______________________________________                                    

(5) Non-treated Control

Surfactant (Product C) was added to each composition, including the non-treated control, at 0.1% of the finished spray.

Six replicates were included for each composition.

The compositions were prepared in deionized water and applied to foliage using a hand-held CO₂ pressurized sprayer fitted with a Teejet 8001 nozzle and delivering the equivalent of 50 gallons per acre (foliar spray to near run-off). A non-treated control (water+surfactant) was included.

Applications were made using a spray pressure of 25 PSI. The spray plot area was 36"×18" and the plants were arranged within the plot area and the application applied by volume (20 ml/plot). The non-treated controls received the equivalent amount of water with surfactant but with no chemical added.

The daily greenhouse temperatures ranged from approximately 65° F. at night to 85° F. during the day. The greenhouse heating was set so that the temperature did not fall below 65° F.

Visual assessments were made of the percent necrosis of the whole plant at three days after treatment. The Barrat-Horsfall rating system was used to estimate the amount of plant injury. This rating system is a weighed, 0 to 11 rating scale with 0 being no injury and 11 being 100% injury. On the seventh day, the fresh weight of the plants were taken by cutting plants within treatment replicates at soil level. The fresh weight of each replicate was recorded.

The effect of the rate of the test composition on plant injury and fresh weight was related to the non-treated control. The Barrat-Horsfall numerical injury ratings were converted to estimated mean percent injury using a conversion table developed by Redman King and Brown, Eli Lilly and Company. All plant fresh data were entered into Quattro PRO WINDOWS (version 6.0) spreadsheet, to calculate mean values. All raw data were analyzed by analysis of variance (ANOVA 2-Way) using Quattro Pro version 6.0 program. If a significant F-Test at p=0.05 was found between the composition concentrations and the observations, then the composition mean values were separated by utilizing LSD mean separation test. ED₂₅ and ED₅₀ (Effective Dose that cause a 25 and 50 percent reduction in the parameter measured) values were determined by regression and probit analysis using Lotus 1,2,3 software.

The results which were obtained in this experimentation was tabulated and is presented in Tables I, II and III below. As may be seen from this data, acetic acid applied alone at 10, 8, 6, 4 and 2% showed a rate responsive effect for both plant injury and plant fresh weight. The highest rate, 10%, of acetic acid alone caused 39% plant injury and 29% reduction in plant fresh weight. An ED₂₅ value of 7.5% was calculated for plant injury; an ED₅₀ value could not be determined. For fresh weight reduction, an ED₂₅ value of 22.7% was extrapolated from the data. Citric acid at the rates tested, 6, 4.8, 3.6, 2.4 and 1.2%, was only weakly active causing only slight injury and no reduction in plant fresh weight. The rates tested were too low to allow an ED₂₅ or an ED₅₀ to be determined for either parameter.

When used in mixtures, acetic acid and citric acid were more effective than either alone and, therefore, synergistic. The synergistic interaction between acetic and citric acid is apparent from a comparison of rate response curves prepared from the raw data and the ED₂₅ values (Table III). Acetic acid alone showed an ED₂₅ of 7.5 for plant injury, citric acid was ineffective at the highest rate tested and the combination had an ED₂₅ of 2.6. This result is an increase in activity of approximately three-fold as compared to acetic acid alone at the same concentration. Similar results were obtained on the effects on fresh weight. Acetic acid alone had little effect on plant weight and an ED₂₅ value was extrapolated to be 22.7; the ED₂₅ for the mixture of acetic acid and citric acid was 9.7, a 2.5 fold increase as compared to activity of acetic acid alone.

Four mixtures of acetic acid and citric acid were tested to determine the effect of modification of their weight ratio on herbicidal activity. Acetic acid was included in each of the test mixtures at a single rate of 4.0%. Citric acid was added to produce the following weight ratios: 1:0.8, 1:0.3, 1:0.2 and 1:0.1. Under the conditions of this test, acidic acid alone at 4.0% provided only minimal activity, causing some phytotoxic effects but no effect on the fresh weight of the plants over the seven day course of the test. It is apparent that the combinations of acetic acid and citric acid are synergistic in all the ratios tested. The most effective combination found in these tests was 1 part acetic acid to 0.8 parts citric acid.

It can be seen, therefore, from these experiments that acetic acid was more effective as a herbicide when mixed with citric acid than when applied alone. Assessment of the percent control showed that synergistic action occurred for control of corn when acetic acid and citric acid were mixed. The herbicidal activity of acetic and citric acid was 2.5 to 3 times greater in combination than either material applied alone. The combination of the two materials was synergistic over a wide range of concentrations. The compositions further showed a growth-regulation capacity, as seen from Table II.

SUMMARY OF DISCLOSURE

In summary of this disclosure, the present invention relates to a novel herbicidal composition comprising synergistic combinations of acetic acid and citric acid, most conveniently provided by vinegar and lemon juice, which are diluted with water to provide the desired herbicidal properties. Modifications are possible within the scope of this invention.

                  TABLE I                                                          ______________________________________                                         SYNERGISTIC HERBICIDAL EFFECTS OF MIXTURES OF                                  ACETIC AND CITRIC ACID. PHYTOTOXICITY RATING OF                                CORN PLANTS THREE DAYS AFTER TREATMENT                                         TREATMENT      RATE (%) AVE. % PHYTO †                                  ______________________________________                                         ACETIC ACID    10.0     45                                                                    8.0      10                                                                    6.0      4                                                                     4.0      3                                                                     2.0      2                                                      CITRIC ACID    6.0      2                                                                     4.8      2                                                                     3.6      2                                                                     2.4      1                                                                     1.2      0                                                      ACETIC + CITRIC                                                                               10.0 + 6.0                                                                              96                                                                    8.0 + 4.8                                                                               79                                                                    6.0 + 3.6                                                                               53                                                                    4.0 + 2.4                                                                               21                                                                    2.0 + 1.2                                                                               4                                                      ACETIC + CITRIC                                                                               4.0 + 3.2                                                                               41                                                                    4.0 + 1.2                                                                               24                                                                    4.0 + 0.8                                                                               14                                                                    4.0 + 0.4                                                                               13                                                     CONTROL        0.0      0                                                      ______________________________________                                          † Injury rated, using BarratHorsfall System, on a 1 to 11 scale         with 0 being no injury and 11 being 100% injury.                         

                  TABLE II                                                         ______________________________________                                         SYNERGISTIC HERBICIDAL EFFECTS OF MIXTURES OF ACETIC                           AND CITRIC ACID. FRESH WEIGHT OF CORN PLANTS SEVEN                             DAYS AFTER TREATMENT                                                           TREATMENT  RATE (%)   AVE. WT (g)                                                                               STD DEV                                       ______________________________________                                         ACETIC ACID                                                                               10.0       1.57       0.51                                                     8.0        2.65       0.58                                                     6.0        1.82       0.48                                                     4.0        2.02       0.74                                                     2.0        2.20       0.39                                          CITRIC ACID                                                                               6.0        2.57       0.48                                                     4.8        2.25       0.50                                                     3.6        2.57       0.51                                                     2.4        2.22       0.33                                                     1.2        2.70       0.53                                          ACETIC     10.0 + 6.0 0.82       0.19                                          +          8.0 + 4.8  2.22       0.42                                          CITRIC     6.0 + 3.6  2.73       0.73                                                     4.0 + 2.4  2.92       1.25                                                     2.0 + 1.2  3.15       1.21                                          ACETIC     4.0 + 3.2  2.65       0.64                                          +          4.0 + 1.2  2.55       0.69                                          CITRIC     4.0 + 0.8  2.63       0.88                                                     4.0 + 0.4  3.67       1.56                                          CONTROL    0.0        2.22       0.39                                          ______________________________________                                    

                  TABLE III                                                        ______________________________________                                         PLANT INJURY AND FRESH WEIGHT, ED.sub.25  AND ED.sub.50  IN % a.i              TREATMENT/PARAMETER  ED.sub.25  ED.sub.50                                      ______________________________________                                         Acetic Acid Alone                                                              Plant Injury         7.5        ND                                             Fresh Weight         22.7 †                                                                             ND                                             Citric Acid Alone                                                              Plant Injury         ND         ND                                             Fresh Weight         ND         ND                                             Acetic + Citric                                                                Plant Injury         2.6        5.3                                            Fresh Weight         5.3        10.5                                           ______________________________________                                          ND = Not Determined                                                            † = Extrapolated Value                                             

What I claim is:
 1. An aqueous herbicidal composition for contact kill of vegetative growth, consisting essentially of acetic acid and citric acid in proportions which provide a synergistic herbicidal activity in comparison to the herbicidal activity of each of the acids alone.
 2. The composition of claim 1 containing a weight ratio of acetic acid to citric acid of about 10:1 to about 0.5:1.
 3. The composition of claim 2 wherein said weight ratio is about 4:1 to about 1:1.
 4. The composition of claim 1 which, in use, contains up to about 10 wt % acetic acid.
 5. The composition of claim 4 wherein said acetic acid is present in an amount of from about 1 to about 5 wt %.
 6. The composition of claim 5 wherein said citric acid is present in an amount of about 0.25 to about 5 wt %.
 7. The composition of claim 1 formulated as concentrate for dilution for use.
 8. The composition of claim 1 wherein a wetting agent also is present in the composition.
 9. The composition of claim 1 in the form of a concentrate comprising:500 mls of vinegar 250 mls of lemon juice 2300 mls of water.
 10. An aqueous composition for contact kill of vegetative growth, consisting essentially of:acetic acid in an amount of from about 2 to about 10 wt %, citric acid in an amount of from about 1 to about 6 wt %, said acetic acid and citric acid being present in a synergistic weight ratio of about 1:0.1 to about 1:0.8, said composition being in fully diluted form ready to apply to post-emergent vegetative growth by spraying onto the vegetative growth.
 11. The composition of claim 10 which further contains up to about 0.5 wt % of a wetting agent.
 12. A method of controlling post-emergent vegetative growth, which comprises applying to said vegetative growth an aqueous herbicidal composition comprising acetic acid and citric acid, said citric acid being present in said composition in a herbicidal activity enhancing amount and said acetic acid and citric acid being present in said composition in proportions sufficient to achieve complete or selective kill of said vegetative growth.
 13. A method of regulating the growth of post-emergent vegetative growth, which comprises applying to said vegetative growth an aqueous composition comprising acetic acid and citric acid, said acetic acid and citric acid being present in said composition in proportions sufficient to achieve a desired degree of control to the growth of said vegetative growth. 